Not too sure about the serial part, and we don't see how you trigger the change of the frameRate, but changing this one isn't a very reliable way to set an animation speed: it is a speed Processing tries to attain, but it might fail (although more on high speeds than on low ones).
delay() is rarely a solution too.
Using millis() time control in draw() (examples abound in the forum) is more precise.
Note that loading the images in delay() (if that's what you do), in a loop (I don't see the point here) is a bad idea, as it slows down a lot the sketch. Better load them in advance in setup(), and use a loop to fill your array (copy/paste is often a bad idea in programming! -- better make the program do repetitive jobs).

You don't have to change the speed at which the images load, but the speed at which the images are displayed!
And you can't change the millis() value, it is changed by the computer's clock... Its value must be used to see if time between two draw() calls is enough to display a new image (supposing the frame rate is indeed much superior to the display rate).

Hi, 

No, use draw() like the body of a loop that Processing manages. Don't loop for wait inside it.
It is more like:

No, set it (frameRate) as high as possible.
Also you can do:

1. for (int i = 0; i < numFrames; i++)
   
2. {
3.   images[i]  = loadImage("PT_anim" + nf(i, 4) + ".gif");
4. }

No, never had an Arduino. Do a println() of timeBetween to check the received values.

ok i think i got it to speed up by setting startTime to a high value. here is my code using a loop input instead of arduino. it's still a bit too fast though, so tweaking some things to see what will work. does it look ok?

Why are you looping inside draw()? The previous version was fine. Here, you just overlap the images, only displaying the last one.